Practice: Which one of the following combinations does not create a buffer?
| Sections | |||
|---|---|---|---|
| Buffer | 50 mins | 0 completed | Learn |
| Acid and Base Titration Curves | 32 mins | 0 completed | Learn |
| Weak Acid Strong Base Titrations | 34 mins | 0 completed | Learn |
| Weak Base Strong Acid Titrations | 17 mins | 0 completed | Learn |
| Strong Acid Strong Base Titrations | 10 mins | 0 completed | Learn Summary |
| Titrations of Diprotic and Polyprotic Acids | 27 mins | 0 completed | Learn |
| Ksp | 58 mins | 0 completed | Learn |
| Additional Practice |
|---|
| Equivalence Point |
| Acid Base Indicators |
| Selective Precipitation |
| Formation Constant |
| Additional Guides |
|---|
| Henderson Hasselbalch Equation (IGNORE) |
Identifying a Buffer
A buffer is a solution composed of a weak acid with its conjugate base.
Concept #1: Understanding a Buffer.
Transcript
Hey guys! In this new video, we're going to take our first looks at what exactly is a buffer and how exactly do they work.
So we're going to say here, solutions that contain a weak acid and its conjugate base. And remember, when I say weak acid we could think of HF. Conjugate base means it has 1 less H+, so take off the H+ you have F-. But professors don't like to give you just F-, they'll combine that F- with a metal, so we could say our conjugate base here is NaF. So solutions which contain a weak acid like HF and a conjugate base has one less H like NaF are called buffer solutions because they resist drastic changes in pH.
Now how do they accomplish this? Well they do this by keeping your H+ concentration and your OH- concentration constant, it keeps them basically the same. The way this works is we're going to say adding a small amount of strong base and the pH will increase because remember if you add base you're going to go above 7, so you keep going up and up. But it's not going to increase by much because the weak acid will neutralize this strong base that you add. Now adding a small amount of strong acid and the pH will decrease. Again, it's not going to decrease by much because why? The conjugate base will neutralize what you add. So that's how a buffer works. Any acid or base that I add they get reacted with either the weak acid or the conjugate base. So remember acid and bases are natural enemies of each other. So if I had base, my weak acid steps in to try to take it out. If I add acid, my conjugate base steps up and tries to take it out. That's how a buffer will work. And remember, the only thing that can destroy a buffer is by adding too much strong base or too much strong acid. Adding water to a base does nothing to it. Well adding water to not a base but a buffer does nothing to it. Why? Because adding water would change the concentration of my weak acid but also change the concentration of my weak base proportionally, so proportionally the ratio would stay the same, so my buffer would be unaffected by the addition of water. So remember, adding a strong acid or base is the only way to really destroy a buffer, adding water does nothing to it.
Now knowing this, I want you guys to try to answer this first Practice Question. We're going to say: Which one of the following combinations does not create a buffer?
Remember we just set up above, a buffer is a weak acid and its conjugate base. So this is going to require you guys to remember the rules that we talked about in identifying compounds that is either being acidic or basic, strong or weak. Once you can do that, you will be able to guide your way to the correct answer for this one. Come back, click on the explanation button and see the choice that I make, and see if it matches up with yours.
Buffers resist drastic changes to the pH if a strong acid or strong base is added.
If a strong base is added then the buffer resists a pH change by having the weak acid neutralize it.
If a strong acid is added then the buffer resists a pH change by having the conjugate base neutralize it.
Practice: Which of the following combinations can result in the formation of a buffer?
Buffer Creation
As we stated earlier a buffer is composed of a weak acid and its conjugate base, but there are actually three ways to create a buffer.
Concept #2: Method 1 for Creating a Buffer.
Transcript
Hey guys! In this new video, we're going to take a look at one of the different ways to create a buffer.
We know what a buffer is, a buffer is made up of a weak acid and conjugate base or a conjugate acid and a weak base, so that's what a buffer is. But there are 3 ways to make a buffer and it's going to be important that you guys recognize these 3 ways.
Now we're going to say the First Way is obvious: A buffer is made up of a weak acid and its conjugate base, so one way to make a buffer is just mixing those two things together.
So we're going to say mixing a weak acid and its conjugate base. So for Example:
What we need to realize here is that we're going to say in this case a good buffer, an ideal buffer, so ideal buffer means that this is the best type of buffer. An ideal buffer is when our weak acid = our conjugate base, they're the same amount. So let's say we have 0.1 M HF and 0.1 M NaF. And we should realize that the numbers could be different for them but they're work best when they're the same. We're going to say this has to do with our buffer range. What you should realize here is a good buffer has to fall within the range of 10:1 or 1:10. Okay, so what do I mean by that? I mean this.. So 10:1 that means our weak acid utmost could only be 10 times more than my conjugate base, if it falls outside that range it will be a bad buffer. So good buffer is between 10:1 ratio or 1:10 ratio. In the 1:10, now the weak acid is 1 and the conjugate base is 10 times that. Okay, so again this is the buffer range, a good buffer falls within this range. If it falls outside that range it'll still be a buffer, it will just be a very bad buffer. And remember, an ideal buffer is the best buffer, that's when both are the same.
Now connected to this also was another topic which is called our buffer capacity. Now we're going to say buffer capacity, all it means is the more concentrated my weak acid and conjugate base, the better my buffer. And this makes sense because remember what is the buffer doing? It's trying to neutralize the strong acid and the strong base that you add to them. And they can't do their job effectively if there's a little bit of them. So to fight such strong acids and strong bases, you need a lot of weak acid and a lot of conjugate base. The more the better, the more they can better defend themselves. So here we're going to say this is good because they're both the same number but this is better because it's more concentrated. So this has a better buffer capacity. So buffer capacity the more concentrated, the better.
Now if we go back to this ideal buffer, we're going to say that's when they both equal each other. We're going to say that this is found at our half-equivalence point. When we reach the half-equivalence point, that's when we have an ideal buffer. We'll talk more on detail on that when we get to titration graphs. When we get to the titration graphs of buffers, we'll take a close look and see what do I mean by the half-equivalence point and why is this an ideal buffer. So just for right now, we'll write a little note on that. An ideal buffer is when they're both equal, this happens at the half-equivalence point. So remember the difference between buffer capacity and buffer range. The best buffer is when they're both equal in amount. The buffer range says they could be a 10:1. Once it's outside that 10:1 ratio, the buffer is still a buffer but it's going to be a bad buffer. It'll get destroyed very quickly by a strong acid or base that we add.
The first and most obvious way to create a buffer is to simply combine a weak acid and its conjugate base. In this case, a buffer is most ideal when both components are highly concentrated and equal to one another.
The weak acid and conjugate base can be different from one another by up to a magnitude of 10. This is called the buffer range. If they are different by more than 10 then this is considered a bad buffer.
Concept #3: Method 2 for Creating a Buffer.
Transcript
Now the Second Way to make a buffer is to mix some strong acid with some weak base. But here's the thing about this type, we're going to say here the weak base has to be higher in amount, must be higher in amount. If the weak base is equal to the strong acid, it'll destroy the buffer. If the strong acid is greater than my weak base, it'll destroy the buffer. So the weak base has to always be higher than the strong acid, otherwise the buffer will be destroyed.
So if we take a look at the Example we can say here:
We have 1 mol of HF and 1.5 mols of NH3. NH3 are weak base and there's more of it. Our units here can be mols or Molarity. In this case this would be a buffer. If we have 1 mol HF and 1 mol NH3, no longer a buffer because the strong species is equal to my weak species. If I have.. Sorry this is HCl actually. HF is a weak acid so disregard that, HCl. And if I have 1.5 mols of HCl and still 1 mol NH3, this will also no longer be a buffer. Your strong species cannot be equal to or greater than your weak species, if it is your buffer gets destroyed, so remember that. The weak species has to be higher in amount than the strong species.
The second method in creating a buffer is mixing a strong acid with a weak base. In this case since we have a strong species mixing with a weak species then we must make sure the weak species is higher in amount.
Concept #4: Method 3 for Creating a Buffer.
Transcript
And then finally the last type, we just said strong acid and weak base. So, let's reverse it, weak acid and strong base. So example here, we could have 1.2, different number, 2.5 0 molar HF now, that's a weak acid and 1.0 molar NaOH, okay? So, now our weak acid is definitely larger in amount. So again, here we need the weak species higher in amount. So, this would be a buffer, got to remember that. So, if we go back first way is to mix weak acid and conjugate base here, they could be equal to or differ from each other but the good buffers are within the range of 10 to one, in the next two the weak species has to be higher than the strong species otherwise it won't be a buffer, you have to remember all three cases because you'll be tested on them and if you don't know which is which you won't be able to get the correct answer. So, just remember, weak acid conjugate base that can be equal that can be different as long as it's within the range of 10 to one it's a good buffer, if it's outside that range it's a bad buffer, case two and three the weak species have to be higher than the strong species, the strong species cannot be equal to or greater, if it is the buffer gets destroyed. Remember these principles and they'll help guide you to see if you have a buffer or not.
The third method in creating a buffer is mixing a strong base with a weak acid. In this case since we have a strong species mixing with a weak species then we must make sure the weak species is higher in amount.
Example #1: Which of the following combinations can result in the formation of a buffer?
a) 0.01 moles HClO (hypochlorous acid) and 0.05 moles of NaOH.
b) 0.01 moles HClO (hypochlorous acid) and 0.05 moles of HCl.
c) 0.01 moles HClO (hypochlorous acid) and 0.05 moles of NH3.
d) 0.01 moles HClO (hypochlorous acid) and 0.001 moles of NaOH
Transcript
Hey guys! In this new video, we're going to put to practice some of the principles we learned in creating a buffer.
So for Example 1 it says: Which of the following combinations can result in the formation of a buffer?
So what we should realize here is in every example we have 0.01 moles of hypochlorus acid (HClO). Now HClO it's an acid, so we know it's some type of acid. It has Oxygen so it's an oxy-acid. And remember if we do the math, 1 Oxygen - 1 Hydrogen gives us 0 left over. So HClO is a weak acid. So every single one of these is a weak acid. And because of that you have to remember what 2 ways can we make a buffer if we have a weak acid? So remember the 2 ways is if we have a weak acid and its conjugate base, and the second way is if we have a weak acid and a strong base. But in the second case, the weak species has to be higher in amount.
So let's take a look at the what's mixing with. Here we have NaOH which is a strong base. Here we have HCl which is a strong binary acid. Here NH3 is a neutral amine, so it's a weak base. And NaOH again is a strong base. So we're looking for the weak acid to be paired up with the conjugate base or the strong base. So automatically these 2 are out because we can't pair up a weak acid with a strong acid or weak acid with a weak base, it has to be a conjugate base or a strong base. Now in the first one we actually have more moles of these strong species, so this would not be a buffer, this would actually destroy the buffer. But for the last one, we have more of the weak species than the strong species, so would be the last one that makes a buffer. So again, remember the 3 principles that we learned in creating a buffer. Apply them to this type of question.
Now for Practice 1:
I want you guys to figure out which one of these combinations will result in a buffer. Here remember the word "of" means multiply. So if you multiply these 2 numbers together you can have to find moles because remember moles = Liters * Molarity so divide each of these by 1000, multiply it by the Molarity to have moles.
You could also keep it in milliliters and multiply times the Molarity but then that will give you millimoles. So I don't know if you guys want to deal with millimoles, it's basically the same thing but you don't have to do it that way. So divide them by a 1000, the mL to get L, multiply times the Molarity to give you moles.
And remember the 3 combinations that can result in the formation of a buffer. So check for each one of these, look to see do you have a weak acid and conjugate base; do you have a weak acid and strong base; or do you have a strong acid and weak base. Look for these combinations, if you don't see them don't bother doing the math. So I recommend looking at each compound first and seeing if they match up with any of these combinations. If they do, look more deeply, look to see does it help to create a buffer. If it doesn't match one of these 3 combinations, don't even bother looking at it, don't do the math at all. And remember one key thing I'll give you guys a hint, you have to find out to make sure you have the correct concentration of your strong bases. What do we say about strong bases? The concentration I give you is depended on how many ions you have of which particular for ions. Doing that will help to get the correct answer.
Once you're done with this, come back and click on the explanation button and watch me explain how to best approach this problem. Good luck guys!
Practice: Which of the following combinations can result in the formation of a buffer?
Practice: A buffer solution is comprised of 50.0 mL of a 0.100 M HC2H3O2 and 60.0 mL of a 0.100 M NaC2H3O2. Which of the following actions would completely destroy the buffer?
Henderson – Hasselbalch Equation
Concept #5: The Henderson – Hasselbalch Equation.
Transcript
Hey guys, in this new video, we’re finally get to see how do we calculate the pH of a buffer. We’re going to say we learned that whenever we had a weak acid or a base, we have to use our favorite friend, the ICE chart in order to find pH or pOH. The great thing is now that we're dealing with buffers, we no longer necessarily need to do an ICE chart. We're going to say anytime we know we have a buffer for sure, we can skip the Ice chart altogether and just use our Henderson – Hasselbalch equation. So, Henderson-Hasselbalch. It's also known as the buffer equation. It says that pH equals pKa plus the log of conjugate base over weak acid. When I say pKa, remember P just means negative log. pKa equals the negative log of Ka. Here when I’m talking about conjugate base or weak acid, the units here can be either in molarity or in moles. It all depends. If they give you only molarity, use molarity. If they give you volumes of a particular molarity, remember the word of means multiply. We’d multiply liters times molarity to give ourselves moles.
Whenever we have a buffer we can skip the ICE Chart and use the Henderson Hasselbalch.
Example #2: What is the pH of a solution consisting of 2.75 M sodium phenolate (C6H5ONa) and 3.0 M phenol (C6H5OH). The Ka of phenol is 1.0 x 10-10.
Transcript
Let's look at this first question and see how exactly do we use it. Here it says: What is the pH of a solution consisting of 2.75 molar sodium phenolate, which is this compound, and 3.0 molar phenol, which is this compound. The Ka of phenol is 1.0 times 10 to the negative 10. What you should realize here is phenol has what? It has H's, non-metals, and oxygen. Phenol is an oxyacid. Use the Math that we've learned. You take the number of oxygens minus by the number of hydrogens. We don't get two oxygens left, so this is a weak oxyacid. We definitely know it’s weak because look at its Ka. Its Ka value is extremely small. If your Ka value is less than 1, you're a very weak acid.
Here we have a weak acid. sodium phenolate has one less H available, so this is the conjugate base. We have a weak acid, we have a conjugate base and therefore, we have a buffer. Because we have a buffer, we need to use the buffer equation, pH equals negative log of Ka plus the log of, now they only gave us the molarity here, so that's what we're going to plug in: 2.75 molar the conjugate base over 3.0 molar, our weak acid. When we plug all that in, we’ll get back the answer of 9.96
Practice: Calculate the pH of a solution formed by mixing 200 mL of a 0.400 M C2H5NH2 solution with 350 mL of a 0.450 M C2H5NH3+ solution. (Kb of C2H5NH2 is 5.6 x 10 -4).
Example #3: What is the buffer component concentration ratio, [Pr - ] / [HPr] , of a buffer that has a pH of 5.11. (The Ka of HPr is 1.30 x 10-5).
Example #4: Over what pH range will an oxalic acid (H2C2O4) / sodium oxalate (NaHC2O4) solution work most effectively? The acid dissociation constant of oxalic acid is 6.0 x 10-2.
a) 0.22 – 2.22 b) 1.00 – 3.00 c) 0.22 – 1.22 d) 2.0 – 4.0
Practice: Determine how many grams of sodium acetate, NaCH3CO2 (MW: 82.05 g/mol), you would mix into enough 0.065 M acetic acid CH3CO2H (MW: 60.05 g/mol) to prepare 3.2 L of a buffer with a pH of 4.58. The Ka is 1.8 x 10-5.
Example #5: Which weak acid-conjugate base combination would be ideal to form a buffer with a pH of 4.74.
a) Cyanic acid and Potassium cynate (Ka = 4.9 x 10-10)
b) Benzoic acid and Lithium benzoate (Ka = 6.3 x 10-5)
c) Acetic acid and Sodium acetate (Ka = 1.7 x 10-5)
d) Ammonium chloride and Ammonia (Ka = 5.56 x 10-10)
e) Formic acid and Cesium formate (Ka = 1.7 x 10-4)
Practice: A buffer solution is made by combining a weak acid with its conjugate salt. What will happen to the pH if the solution is diluted to one-fourth of its original concentration?
Progress
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Videos in Buffer
Concept #1: Understanding a Buffer.
Practice #1: Which one of the following combinations does no...
Practice #2: Which of the following combinations can result ...
Concept #2: Method 1 for Creating a Buffer.
Concept #3: Method 2 for Creating a Buffer.
Concept #4: Method 3 for Creating a Buffer.
Example #1: Which of the following combinations can result i...
Practice #3: Which of the following combinations can result ...
Practice #4: A buffer solution is comprised of 50.0 mL of a ...
Concept #5: The Henderson Hasselbalch Equation.
Example #2: What is the pH of a solution consisting of 2.75 ...
Practice #5: Calculate the pH of a solution formed by mixing...
Example #3: What is the buffer component concentration ratio...
Example #4: Over what pH range will an oxalic acid (H2C2O4) ...
Practice #6: Determine how many grams of sodium acetate, NaC...
Example #5: Which weak acid-conjugate base combination would...
Practice #7: A buffer solution is made by combining a weak a...
Additional Problems
Which of the following acids and their conjugate base would form a buffer with a pH of 8.10?
A. HClO3 pKa= 7.54
B. H2SO3 pKa= 1.77
C. HC2H3O2 pKa= 4.74
D. HNO2 pKa= 3.34
E. HIO pKa= 10.64
A buffer is prepared using 0.085M formic acid and 0.085M sodium formate. Which of the following statements is false?
An aqueous solution contains 0.26M hydrocyanic acid, HCN. One liter of this solution could be converted to a buffer by the addition of:
A buffer:
a. can be made by a combination of a strong acid and strong base.
b. can be a combination of a weak acid and its conjugate base.
c. resists changes in pH.
d. both A and C
e. both B and C
Which weak acid-conjugate base combination would be the best to create a solution with a pH of 7.538?
a) Butanoic acid and Potassium butanoate (Ka = 1.5 x 10 -5)
b) Benzoic acid and Sodium benzoate (Ka = 6.3 x 10 -5)
c) Acetic acid and Lithium acetate (Ka = 1.8 x 10 -5)
d) Ammonium chloride and Ammonia (Kb = 1.8 x 10 -5)
e) Hypochlorous acid and sodium hypochlorite (Ka = 2.9 x 10 -8)
Which of the following is TRUE?
a) An effective buffer has a [base]/[acid] ratio in the range of 10 - 100.
b) A buffer is most resistant to pH change when [weak acid] = [conjugate base]
c) An effective buffer has very small absolute concentrations of weak acid and conjugate base.
d) A buffer cannot be destroyed by adding too much strong base, it can only be destroyed by adding too much strong acid.
e) None of the above are true.
Which of the following combinations can result in the formation of a buffer?
a) HBr and NH4Cl
b) LiOH and HNO3
c) H3PO4 and LiH2PO4
e) None of these combinations result in a buffer.
To create a buffer that maintains a pH around 7.54, which solution would you choose?
A. CH3COOH and NaCH3COO
B. HClO and KClO
C. NaOH and HCN
D. HNO3 and KNO3
What is the pH of a solution that is 0.2 M in acetic acid (Ka= 1.8 x 10 -5) and 0.2 M in sodium acetate?
A. 4.7
B. 9.3
C. 7.0
D. 5.4
E. 8.6
Consider a solution consisting of the following two buffer systems:
H2CO3 ⇌ HCO3 - + H + pKa = 6.4
H2PO4 - ⇌ HPO4-2 + H + pKa = 7.2
At pH 6.4, which one of the following is TRUE of the relative amounts of acid and conjugate base present?
A) [H2CO3] = [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ]
B) [H2CO3] > [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ]
C) [H2CO3] = [HCO3 - ] and [HPO4 -2 ] > [H2PO4 - ]
D) [HCO3 - ] > [H2CO3] and [HPO4 -2 ] > [H2PO4 - ]
E) [H2CO3] > [HCO3 - ] and [HPO4 -2] > [H2PO4 -]
How many moles of solid NaF would have to be added to 1.0 L of 1.90 M HF solution to achieve a buffer of pH 3.35? Assume there is no volume change.
(Ka for HF = 7.2 x 10 -4)
A. 3.1
B. 2.3
C. 1.6
D. 1.0
E. 4.9
A solution was made by dissolving 0.1219 moles of sodium acetate in 200.0 mL of 1.00 M acetic acid. Assuming the change in volume when the sodium acetate is not significant, estimate the pH of the solution. The Ka for acetic acid is 1.7 x 10-5.
A. 5.42
B. 7.31
C. 9.42
D. 4.56
E. 2.89
How many moles of solid NaF would have to be added to 1.0 L of 1.90 M HF solution to achieve a pH of 3.35? Assume there is no volume change.
(Ka for HF = 7.2 x 10 -4)
Calculate the pH of a buffer that is 0.225 M HC 2H3O2 and 0.162 M KC2H3O2. The Ka for HC2H3O2 is 1.8 × 10-5.
A) 4.89
B) 9.11
C) 4.74
D) 9.26
E) 4.60
Which of the following is TRUE?
A) An effective buffer has a [base]/[acid] ratio in the range of 10 - 100.
B) A buffer is most resistant to pH change when [acid] = [conjugate base]
C) An effective buffer has very small absolute concentrations of acid and conjugate base.
D) A buffer can not be destroyed by adding too much strong base. It can only be destroyed by adding too much strong acid.
E) None of the above are true.
Which of the following solutions is a good buffer system?
A) A solution that is 0.10 M NaCl and 0.10 M HCl
B) A solution that is 0.10 M HCN and 0.10 M LiCN
C) A solution that is 0.10 M NaOH and 0.10 M HNO 3
D) A solution that is 0.10 M HNO3 and 0.10 M NaNO 3
E) A solution that is 0.10 M HCN and 0.10 M KI
Calculate the pH of a buffer that is 0.145M in acetic acid and 0.202M in sodium acetate. The acid dissociation constant for acetic acid 1.75x10 –5.
4.60
4.89
5.05
4.74
9.01
Calculate the pH of a solution that is 0.210M in nitrous acid and 0.290M in potassium nitrite. The acid dissociation constant of nitrous acid is 4.50x10 –4.
3.21
3.49
13.86
10.51
4.56
Which of the following acids and their conjugate base would form a buffer with a pH of 8.10?
HClO3 pKa = 7.54
H2SO3 pKa = 1.77
HC2H3O2 pKa = 4.74
HNO2 pKa = 3.34
HIO pKa = 10.64
Which one of the following pairs, when mixed, do not form a buffered solution?
a) 1.0 M CH3CH2NH2/1.0 M CH3CH2NH3Cl
b) 1.0 M CH3CH2COOH/1.0 M CH3CH2COONa
c) 1.0 M KOH/1.0 M HI
d) 1.0 M NH3/1.0 M NH4Cl
e) 1.0 M H3PO4/1.0 M KH2PO4
The pH of a sodium acetate-acetic acid buffer is 4.50. Calculate the ratio of [CH3COO- ]/[CH3COOH].
A student is asked to prepare a buffer solution at pH = 8.60 using one of the following weak acids: HA (Ka = 2.7 x 10-3), HB(Ka= 4.4x10-6), HC (Ka = 2.6 x 10-9), Which acid should she choose?
What is the effective pH range of the pyridine/pyridinium chloride buffer? For pyridine, the value of Kb is 1.8 x 10-9.
(a) 9.1-11.1
(b) 1.4-3.4
(c) 10.3-12.3
(d) 7.7-9.7
(e) 4.3-6.3
What is the pH of a solution of 0.46 M acid and 0.36 M of its conjugate base if the pKa is 5.51?
a) 4.70
b) 4.90
c) 5.20
d) 5.40
e) 5.62
If a biochemist wishes to prepare a buffer that will be effective at a pH of 3.0 (at 25°C) for studying peptide degradation, what will be the best choice for the acid component?
(a) Oxalic acid (H2C2O4), Ka = 5.9 x 10 -2
(b) Hydrofluoric acid (HF), Ka = 6.6 x 10 -4
(c) Pyridinium ion (HC5H5N+ ), Ka = 5.6 x 10 -6
(d) Hypochlorous acid (HClO), Ka = 3.0 x 10 -8
(e) Hydrocyanic acid (HCN), Ka = 6.17 x 10 -10
Which one of the following pairs of substances cannot be mixed together (in any quantities) to form a buffer solution?
(a) H3PO4, KH2PO4
(b) NH3, NH4Cl
(c) HNO2, NaNO2
(d) CH3COONa, CH3COOHa
(e) HNO3, KOH
What is the pH of a solution which is 0.400 M in dimethylamine (CH 3)2NH) and 0.600 M in dimethylamine hydrochloride (CH3)2NH2+Cl−)? Kb for dimethylamine = 0.00074.
1. 10.78
2. 2.95
3. 10.87
4. 3.31
5. 10.69
6. 11.05
7. 11.21
How much sodium lactate NaC3H3O3, should be added to 583.58 mL of a 0.473 M lactic acid, HC3H3O3, solution to make a buffer of pH 4.08? (assume any change in volume is insignificant and that the pKa is rounded to two significant figures)
a. 6.986 grams
b. 1.157 grams
c. 127.4 grams
d. 17.89 grams
e. 51.59 grams
Which of the following weak acids would be BEST to use to make a buffer of pH = 2.90
a. lactic
b. butanoic
c. chloroacetic
d. benzoic
e. hypochlorous
Which of the following weak acids would be BEST to use to make a buffer of
pH = 3.52?
a. nitrous acid
b. hydrofluoric acid
c. chloroacetic acid
d. lactic acid
e. benzoic acid
Two compounds, HA & HB have the same K a value. If a solution is prepared containing 0.5 mole of HA and 0.5 of NaB which of the following is True?
A) The solution pH = pKa but it has no Buffer Capacity
B) The solution is not a Buffer because there is no conjugate base of A or conjugate acid of B-.
C) This solution is a good Buffer because the [weak base] = [weak acid]
D) The pH = pKb for the B-
E) It is not possible to determine if this is a good buffer or not.
Identify a good buffer.
A) small amounts of both a weak acid and its conjugate base
B) significant amounts of both a strong acid and a strong base
C) small amounts of both a strong acid and a strong base
D) significant amount of both a weak acid and a strong acid
E) significant amounts of both a weak acid and its conjugate base
You wish to prepare an HC 2H3O2 buffer with a pH of 4.24. If the pK a of is 4.74, what ratio of C2H3O2- / HC2H3O2 must you use?
A) 0.10
B) 0.50
C) 0.32
D) 2.0
E) 2.8
Explain why the salt of a weak acid, as well as the acid itself, must be present to form a buffer solution.
1. The anion from the salt is needed to partially neutralize added base.
2. The anion from the salt is needed to partially neutralize added acid.
3. The cation from the salt is needed to partially neutralize added acid.
4. The cation from the salt is needed to partially neutralize added base.
5. Actually, a weak acid by itself is a buffer; no salt is needed.
A buffer solution is made by combining a weak acid with its conjugate salt. What will happen to the pH if the solution is diluted to one-half of its original concentration?
a) The pH will increase.
b) The pH will decrease.
c) The pH will remain constant.
d) The solution will become more neutral.
Over what pH range will an oxalic acid (H 2C2O4) / sodium oxalate (NaHC2O4) solution work most effectively? The acid dissociation constant of oxalic acid is 6.0 x 10-2.
a) 0.22 – 2.22 b) 1.00 – 3.00 c) 0.22 – 1.22 d) 2.0 – 4.0
Find the pH of a buffer solution made by mixing 100 mL of 0.20 M methylamine, CH3NH2, with 250.0 mL of a 0.50 M CH 3NH3Cl. Kb of methylamine is 4.4 x 10-4.
Which of the following buffer systems would you use to create a buffer with a pH of 4.0? The Ka of nitrous acid, HNO2 is 4.5 x 10-4.
a) 0.30 M HNO2 / 0.22 M NaNO2
b) 0.22 M HNO2 / 0.30 M NaNO2
c) 0.11 M HNO2 / 0.50 M NaNO2
d) 0.50 M HNO2 / 0.11 M NaNO2
e) 0.30 M HNO2 / 0.30 M NaNO2
Determine how many grams of potassium hypochlorite, KClO (MW: 90.55 ), you would mix into enough 0.055 M hypochlorous acid, HClO (MW: 52.46 ) to prepare 5.0 L of a buffer with a pH = 6.77. Ka of HClO is 2.9 x 10-8.
Which one of the following combinations CANNOT function as a buffer solution?
A) H2C2O4 and CsHC2O4 D) HF and LiF
B) NH3 and (NH4)2SO4 E) HCl and NaCl
C) K2HPO4 and KH2PO4
Calculate the pH of a buffer solution that contains 0.25 M chloroacetic acid (ClCH2CO2H) and 0.15 M sodium chloroacetate (ClCH2CO2Na). [Ka = 1.4 × 10–3 for chloroacetic acid]
A) 3.07 B) 2.85 C) 4.19 D) 2.63 E) 4.41
You are asked to go into the lab and prepare a buffer solution with a pH of 6.40 ± 0.2. Which weak acid would be the best choice?
A) carbonic acid Ka = 4.2 x 10-7
B) phenol Ka = 1.3 x 10-10
C) ascorbic acid Ka = 8.0 x 10-5
D) hydrosulfuric acid Ka = 9.5 x 10-8
E) potassium hydrogen phthalate Ka = 3.1 x 10-6
Which of the following procedures will result in the largest change in pH?
Adding NaNO2 to a solution of HNO2 in water
or
Adding NaNO3 to a solution of HNO3 in water
Blood contains a buffer of carbonic acid (H2CO3) and hydrogen carbonate ion (HCO3-) that keeps the pH at a relatively stable 7.40. What is the ratio of [HCO3-] / [H2CO3] in blood? Ka1 = 4.30x10-7 for H2CO3.
0.0926
10.8
3.98 x 10-8
1.71 x 10-14
To create a buffer that maintains a pH around 7.54, which solution would you choose?
A. CH3COOH and NaCH3COO
B. HClO and KClO
C. NaOH and HCN
D. HNO3 and KNO3
The addition of hydrochloric acid and __________ to water produces a buffer solution.
a. HC6H5O
b. NaOH
c. NH3
d. HNO3
e. NaNO3
A buffer solution is comprised of 50.0 mL of a 0.100 M HC 2H3O2 and 60.0 mL of a 0.100 M NaC2H3O2. Which of the following actions would completely destroy the buffer?a) Adding 0.003 mol HC2H3O2b) Adding 0.007 mol Ca(C2H3O2)2 c) Adding 0.005 mol NaHd) Adding 0.004 mol HNO3e) Adding 0.001 mol HNO3
Which of the following combinations can result in the formation of a buffer?a) 90 mL of 0.10 M HCN with 70 mL of 0.10 M NH 3.b) 70 mL of 0.10 M HC 2H3O2 with 30.0 mL of 0.15 M Ba(OH) 2.c) 50 mL of 0.10 M HNO3 with 50 mL of 0.10 M NaOH.d) 70 mL of 0.10 M HNO2 with 25 mL of 0.10 M LiH.e) 70 mL of 0.10 M HClO with 70 mL of 0.10 M LiOH.
Which of the following acids and their conjugate base would form a buffer with pH of 3.34?HClO Ka = 2.9 x 10 –8C6H5CO2H Ka = 6.5 x 10 –5HF Ka = 3.5 x 10 –4HIO3 Ka = 1.7 x 10 –1HClO2 Ka = 1.1 x 10 –2
What is the pH of a solution prepared by mixing 0.250 mol of benzoic acid (C6H5COOH, Ka=6.50 x 10 –5) and 0.150 mol of sodium benzoate (C6H5COONa) in sufficient water to yield a 1.00 L solution?
a) 3.965
b) 4.190
c) 4.411
d) 7.321
e) 10.084
Which solution has the greatest ability to resist a change in pH (or buffering capacity)? a) 0.543 M NH3 and 0.555 M NH4 Clb) 0.087 M NH3 and 0.088 M NH4 Clc) 0.234 M NH3 and 0.100 M NH4 Cld) 0.100 M NH3 and 0.455 M NH4 Cle) They are all buffer solutions and would all have the same capacity.
The addition of hydrochloric acid and __________ to water produces a buffer solution.a) HC6H5Ob) NaOHc) NH3d) HNO3e) NaNO3
Calculate the pH of a solution created by mixing 168.9 mL of 0.395 M Butanoic acid, HC4H7O2, with 293.8 mL of 0.189 M Potassium hydroxide, KOH. The K a of butanoic acid is 1.5 x 10-5. a. 5.52b. 5.14c. 4.90d. 4.74e. 4.50
Which weak acid-conjugate base combination would be the best to create a solution with a pH of 4.193? a) Butanoic acid and Potassium butanoate (Ka = 1.5 x 10-5) b) Benzoic acid and Sodium benzoate (Ka = 6.3 x 10-5) c) Acetic acid and Lithium acetate (Ka = 1.8 x 10-5) d) Ammonium chloride and Ammonia (Kb = 1.8 x 10-5) e) Hypochlorous acid and sodium hypochlorite (Ka = 2.9 x 10-8)
A certain aqueous HCNO solution has a pH of 2.17. If solid KCNO is added to the solution, will the pH increase, decrease, or remain the same? Assume that there is no volume change upon addition of KCNO.
Which of the following molar ratios is the correct equilibrium ratio of BASE: ACID for a solution made of aniline (Kb = 3.8 x 10-10) and anilinum nitrate where the pH is 4.80?
1. 1:2
2. 3:5
3. 7:2
4. 2:1
5. 5:3
6. 4:1
7. 9:1
Which of the following pairs of solution does not produce a buffer?A. 0.3 M HClO3 & 0.2 M KOHB. 0.2 M NH3 & 0.1 M HClO4C. 1.5 M HF & 1 M LiOHD. 0.1 M KCOOH & 0.1 M NaCOOH
What is the pH of a buffer solution that contains 0.55 M methylamine, CH3NH2, and 0.29 M of methylammonium chloride, CH3NH3Cl?A. 3.63B. 10.32C. 10.92D. 10.37E. 3.08
Which pair of substance can be dissolved together (in the right ratio) to prepare a buffer solution?i, C2H3O2Hii. NaC2H3O2iii. NaOHiv. HClv. NaClA. i and iiB. i and iiiC. ii and iiiD. i and ii, ii and iv, i and iiiE. iv and v; i and iii
Calculate the pH of a solution made by mixing 8.627 g of sodium butanoate in enough 0.452 M butanoic acid, HC4H7O2 , to make 250.0 mL of solution.A. 4.75B. 4.82C. 5.00D. 2.58E. 4.65
Which of the following solutions is a good buffer system?A) A solution that is 0.10 M HC2H3O2 and 0.10 M LiC2H3O2B) A solution that is 0.10 M HBr and 0.10 M KC 2H3O2C) A solution that is 0.10 M HI and 0.10 M NH 4+D) A solution that is 0.10 M NaOH and 0.10 M KOHE) None of the above are buffer systems.
Calculate the pH of a buffer that is 0.225 M HC 2H3O2 and 0.162 M KC2H3O2. The Ka for HC2H3O2 is 1.8 × 10-5.
Which pair of compounds will form a buffer in aqueous solution?
A. HCl and NaOH
B. NaCN and KCN
C. HCN and HCl
D. HCN and NaCN
E. NaCN and NaOH
F. HCl and NaCl
Which pair of compounds will form a buffer in aqueous solution?
a. HCl and NaOH
b. NaCN and KCN
c. HCN and HCl
d. HCN and NaCN
e. NaCN and NaOH
Which pair of compounds will form a buffer in aqueous solution?a. HCN and NaCNb. HCl and NaOHc. NaCN and NaOHd. HCN and HCle. HCl and NaClf. NaCN and KCN
What mass of solid NaCH3CO2 (molar mass=82.0 g/mol) should be added to 1.0 L of 0.50 M CH3CO2H to make a buffer with a pH of 7.21? (pKa of CH 3CO2H = 7.21)
What mass of ammonium chloride, NH 4Cl, (Ka = 5.6 x 10 -10) must be added to exactly 500mL of 0.10M NH3 solution to give a solution with a pH of 9.00?
Which one of the following pairs cannot be mixed together to form a buffer solution? Why?a. NH3, NH4Clb. NaC2H3O2, HCl (C2H3O2- = acetate)c. RbOH, HBrd. KOH, HFe. H3PO4, KH2PO4
The addition of hydrofluoric acid and __________ to water produces a buffer solution. Why / how?a. HClb. NaNO3c. NaFd. NaCle. NaBr
Of the following, which is the best base to create a buffer with a pH = 8.0?a. Aniline, Kb = 4.3 x 10-10b. Ethylamine, Kb = 6.4 x 10-4c. Hydrazine, Kb = 1.3 x 10-6d. Pyridine, Kb = 1.7 x 10-9
Which of the following solutions is a buffer? Check all that apply.a. A solution made by mixing 100 mL of 0.100 M HCOOH and 500 mL of 0.100 M NaOH.b. A solution made by mixing 100 mL of 0.100 M HCOOH and 50 mL of 0.100 M NaOH.c. A solution made by mixing 100 mL of 0.100 M HCOOK and 50 mL of 0.100 M KCl.d. A solution made by mixing 100 mL of 0.100 M HCOOH and 50 mL of 0.100 M HCl.
Which of the following solutions could be classified as a buffer?a. 0.100 M HCl and 0.100 M NH4Clb. 0.100 M HBr and 0.100 M KBrc. 0.100 M HNO2 and 0.100 M NaNO2d. 0.100 M HCl and 0.100 M NaOH
Determine whether or not the mixing of each of the two solutions indicated below will result in a buffer:75.0 mL of 0.10M HF 55.0 mL of 0.15 M NaF
75.0 mL of 0.10 M HF; 55.0 mL of 0.15 M NaFa. this will be a bufferb. this will not be a buffer
150.0 mL of 0.10 M HF; 135.0 mL of 0.175 M HCla. this will be a bufferb. this will not be a buffer
165.0 mL of 0.10 M HF; 135.0 mL of 0.050 M KOHa. this will be a bufferb. this will not be a buffer
125.0 mL of 0.15 M CH3NH2; 120.0 mL of 0.25 M CH3NH3Cl a. this will be a bufferb. this will not be a buffer
105.0 mL of 0.15 M CH3NH2; 95.0 mL of 0.10 M HCla. this will be a bufferb. this will not be a buffer
At a pH of 7.40, what is the ratio of the molar concentrations of PO 43− to HPO42−?Express your answer using two significant figures.
At a pH of 7.40, what is the ratio of the molar concentrations of H 2PO4− to H3PO4?Express your answer using two significant figures.
At a pH of 7.40, what is the ratio of the molar concentrations of CO 32− to HCO3−?Express your answer using two significant figures.
At a pH of 7.40, what is the ratio of the molar concentrations of HCO 3− to H2CO3?Express your answer using two significant figures.
Find the ratio of the volumes of NaC 3H5O3 soloution to HC3H5O3 (lactic acid) required to prepare a buffer with a pH of 3.90. The solutions are equal in molarity. Ka = 1.4x10-4 for HC3H5O3.
CN– is the conjugate base to the weak acid HCN, with Ka = 6.0 × 10–10, pKa = 9.22.Given a 50 mL of a 0.1 M of NaCN (which dissociates completely), how many mL of 1.0 M HCl should be added to the solution in order to to bring the pH to 9.22?
Complete this table of initial and final concentrations. HF(aq) + KOH(aq) → KF(aq) + H 2O(l)Initial: 2.0 M 1.0M 0MFinal:Which of the following best describes the final solution?a. a neutral salt solutionb. a bufferc. none of the above
The Ka values for nitrous acid (HNO2) and hypochlorous (HCIO) acid are 4.5 x 10 -4 and 3.0 x 10 -8 respectively.What other substance containing sodium would be needed to make the buffer? Express your answer as a chemical formula.
A buffer solution contains 0.323 M KHSO3, and 0.257 M K2SO3.If 0.0495 moles of sodium hydroxide are added to 250. mL of this buffer, what is the pH of the resulting solution?(Assume that the volume does not change upon adding sodium hydroxide)pH =
You need to prepare 100.0 mL of a pH = 4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.180 M sodium benzoate. How much of each solution should be mixed to prepare this buffer?
Calculate the pH of a solution that is 0.230 M in benzoic acid and 0.130 M in sodium benzoate, a salt whose anion is the conjugate base of benzoic acid.
Of the following solutions, which has the greatest buffering capacity?a. 0.100 M NH3 and 0.455 M NH4CIb. 0.087 M NH3 and 0.088 M NH4CIc. They are all buffer solutions and would all have the same capacity.d. 0.234 M NH3 and 0.100 M NH4CIe. 0.543 M NH3 and 0.555 M NH4CI
Which of the following buffer systems would be the best choice to create a buffer with pH = 9.05? a. HF / KFb. HNO2 / KNO2c. NH3 / NH4Cld. HClO / KClO
Which of the following solutions is a good buffer system?a. A solution that is 0.10 M HC2H3O2 and 0.10 M LiC2H3O2b. A solution that is 0.10 M HF and 0.10 M NaC 2H3O2c. A solution that is 0.10 M NaOH and 0.10 M KOHd. A solution that is 0.10 M HCl and 0.10 M NH 4+e. None of the above are buffer systems
A solution contains 1.00 mole of acetic acid and has pH = 2.50. How many grams of NaCH3COO·3H2O (of MW 136) should be dissolved in the solution to raise the pH to 4.00?1. 10 g2. 35 g3. 20 g4. 15 g5. 24 g
How could you make a buffer? Select all that apply.a) Partially neutralize a weak base solution by addition of a strong acid.b) Add appropriate quantities of weak acid and its conjugate base to water.c) Partially neutralize a strong acid solution by addition of a strong base.d) Partially neutralize a weak acid solution by addition of a strong base.e) Partially neutralize a strong base solution by addition of a strong acid.
Which of the following statements are TRUE of buffer solutions?1. A buffer solution can be made by mixing equal concentrations of acetic acid and sodium acetate.2. A buffer solution can be made by mixing equal concentrations of hydrochloric acid and sodium chloride.3. A buffer solution resists changes in pH when small quantities of acid or base are added.a. 1 and 3 onlyb. 1 and 2 onlyc. 2 and 3 onlyd. All of 1, 2, and 3e. None of 1, 2, and 3
Which set of compounds would form a buffer in aqueous solution?HBr and NaBrHCl and HClONaF and KFHF and KFNaF and NaOHNaCl and KClHCN and NaCN
a) Calculate the percent ionization of a 0.16M benzoic acid solution in pure water.b) Calculate the percent ionization of a 0.16M benzoic acid solution in a solution containing 0.11M sodium benzoate.
The Ka of nitrous acid, HNO2, is 4.5x10-4. What [NO2-]/[HNO2] ratio is necessary to make a buffer with a pH of 3.71?a) 1.9 x 10-8b) 0.45c) 0.76d) 1.5e) 2.3
Calculate the ratio of CH3NH2 to CH3NH3Cl required to create a buffer with pH = 10.28. Express your answer using two significant figures.
a) The Ka for acetic acid (H3CCO2H) is 1.737 x 10-5. What is the pKa for this acid? b) use the pKa calculated above to determine the pH at which [H3CCO2H] = [H3CCO2-]
A buffer solution is made using a weak acid, HA, that has a pK a of 6. If the pH of the buffer is 8, what is the ratio of A- to HA?
What mass of ammonium chloride (NH 4Cl, molar mass 53.5g/mol) must be added to a 0.500mL solution of 0.250M ammonia to make a buffer with a pH of 9.26?
Nitric acid, HNO2 is a weak acid with Ka= 4.5 x 10-4. It dissociates according to:HNO2 (aq) ⇌ H+(aq) + NO2-(aq)a.) What is the pH of a buffer solution which is 0.80 M in NO2- and 0.40 M in HNO2? b.) What will be the pH of the resulting solution when 2.0 mL of 0.5 M HCl are added to 50 mL of this (from part a) buffer solution? c.) What will be the pH of the resulting solution when 2.0 mL of 0.5 M NaOH are added to 50 mL of this (from part a) buffer solution?
Which of the following solutions is a buffer?a. A solution made by mixing 100 mL of 0.100 M KClO and 50 mL of 0.100 M KCl.b. A solution made by mixing 100 mL of 0.100 M HClO and 500 mL of 0.100 M NaOH.c. A solution made by mixing 100 mL of 0.100 M HClO and 50 mL of 0.100 M NaOH.d. A solution made by mixing 100 mL of 0.100 M HClO and 50 mL of 0.100 M HCl.
A 100.0 mL buffer solution is 0.175 M in HClO and 0.150 M in NaClO. What is the pH after addition of 0.090 g of NaOH?
The Ka of acetic acid is 1.8 x 10-5 at 25°C.a) What is the pH of a 0.5 M solution of acetic acid at 25°C?b)What is the pH of a solution made up of 20 mL of 0.5 M solution of acetic acid and 10 mL of 0.5 M sodium acetate?c) If 10 mL of 0.1 M NaOH is added to the solution in part b, what is the final pH?d) What is the pH of a solution containing equal concentrations of acetic acid and sodium acetate?
What is the pH change of a 0.210 M solution of citric acid (pKa = 4.77) if citrate is added to a concentration of 0.125 M with no change in volume? Express the difference in pH numerically to two decimal places.
A buffer solution is made using a weak acid. HA, that has a pKa of 5. If the pH of the buffler is 6, what is the ratio of A- to HA?
Benzoic acid (C7H6O2) is a weak acid whose Ka is 6.5 x 10-5. If 0.490 g of benzoic acid are dissolved in 250 ml of water what mass of sodium benzoate (NaC7H5O2) would need to be added to adjust the pH of of the solution to 5.20? (You may assume that the added sodium benzoate doesn't significantly change the solution volume).
Which pair of compounds will form a buffer in aqueous solution?a. NaCN and NaOHb. NaCN and KCNc. HCl and NaOHd. HCN and NaCNe. HCN and HClf. HCl and NaCl
Of the following solutions, which has the greatest buffering capacity?a. 0.296 M HF and 0.122 M NaFb. 0.195 M HF and 8.02 x 10−2 M NaFc. 0.591 M HF and 0.243 M NaFd. 1.18 M HF and 0.486 M NaFe. They are all buffer solutions and would all have the same capacity.